3D touch is like a right-mouse button that provides a drop-down list of choices on a touchscreen. A light touch on a notification or icon lets the user peek at

3D touch is like a right-mouse button that provides a drop-down list of choices on a touchscreen. A light touch on a notification or icon lets the user peek at content and, with a little longer press, it pops open to an expanded view. Lifting the finger lets the view collapse back to the original view. A light touch on a link contained in a message will open it at the top of the screen in Safari.